Ionic liquids, due to their unique attributes, are a new generation of high performance solvents useful for catalytic and separation applications. Ionic liquid-based reactions are considered to be “green” compared to conventional solvents because they possess superior properties; they have relatively low vapor pressures, tend to be non-flammable or essentially non-combustible below their decomposition temperature, have excellent thermal stability with a wide range of tunable liquid properties, and are superior solvents for a diverse array of compounds. The ionic liquids' properties result in liquid carriers that provide operational flexibility and minimize the environmental footprint of a process.
For catalysis systems in ionic liquids, the ionic liquid can act as a solvent (liquid carrier) and/or as a catalyst to stabilize reaction intermediates. However, a major barrier hindering industrial use of ionic liquids is the high costs; the ionic liquid cost is often greater than the reaction product mixture and desired product cost itself. For a practical process, the ionic liquid should be recovered from the reaction mixture for re-use at a very high recovery rate (greater than 80% or 90% or most likely greater than 99 or 99.9%).
The separation technologies currently in use in such ionic liquid catalysis process systems are distillation, vacuum distillation or extraction. Those techniques provide low separation efficiency for many desired products, are not readily scalable to a commercial level, have an unacceptable effect on the environment, and/or are not safe for workers. In addition, certain of the currently used techniques require raising reaction mixtures to boiling temperatures and/or cooling the same-energy intensive activities harmful to the environment and costly on a commercial scale. In distillation processes the required heating levels of the reaction product mixture necessary to cause separation also result in many side reactions that are detrimental to recovery of product, feed, catalyst, and/or the ionic liquid. Extraction processes use particular organic solvents and apparatus that cause the process not only to be more complicated on a commercial scale (as opposed to lab bench processes) but also produce undesirable solvent waste.
Hydroxymethylfurfural (HMF) is a key intermediate chemical and is a flexible platform for producing chemicals and fuels that can substitute for today's petroleum-derived reaction product mixtures. Recent developments have been made in processes for the production of HMF on a commercial scale and at costs that allow petroleum reaction product mixture substitution in the production of major chemicals from biomass and biobased fuels. Scientists at Pacific Northwest National Laboratories have developed a number of inventions demonstrating catalytic conversion of sugars to HMF at high selectivities and conversions using a soluble catalyst in ionic liquid solvents. Such processes require a separation of unreacted sugars, HMF and ionic liquids.
Efficient, cost effective and environmentally sound separation processes for ionic liquid catalysis process systems are needed to recover important reaction components such as the ionic liquids as well as the reaction product and byproducts and allow for the recycling of the ionic liquid on a commercially economically and environmentally acceptable scale.